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As an initial step in studying the mechanism of feedback inhibition of adrenocorticopic hormone (ACTH) by glucocorticoids, the effect of these steroid hormones on ACTH production was studied in AtT-20, a cloned mouse pituitary tumor cell line grown in tissue culture. ACTH levels in cells and medium were measured by bioassay in the hypophysectomized rat and found to be depressed after treatment with dexamethasone, triamcinolone, corticosterone and cortisol, but not significantly affected by nonglucocorticoid hormones. The reduction of both intracellular and extracellular ACTH suggested a primary effect of glucocorticoids on ACTH synthesis. The steroid effects were produced without any detectable change in cell number or total protein levels, suggesting a specific effect on ACTH. This single cell system promises to be a valuable tool for further studies on factors regulating the synthesis and secretion of ACTH. (Endocrinology93: 411, 1973)
Watanabe et al. (1973) studied this question.